Tuolumne Weather Concern this Weekend (7/29 & 30)?


Original Post
dylan grabowski · · Oakland · Joined Mar 2015 · Points: 55

Howdy folks. 

20% chance of t-storms after 11 am on both Saturday and Sunday this weekend. Not super psyched about the forecast.

Planning on Cathedral and Tenaya.

Do you think 20% is too much to worry about? Should we definitely plan on being down before 11 am? 

Cheers!

Dylan

Marc801 C · · Sandy, Utah · Joined Feb 2014 · Points: 65
dylan grabowski wrote:

Howdy folks. 

20% chance of t-storms after 11 am on both Saturday and Sunday this weekend. Not super psyched about the forecast.

Planning on Cathedral and Tenaya.

Do you think 20% is too much to worry about?

The standard Sierra forecast for almost every day in the summer is after 2p, so perhaps a little more iffy.

 Should we definitely plan on being down before 11 am? 

You could safely push that assuming you keep an eye on the weather. Just remember things can change quickly.

wsperry · · San Jose/Lafayette · Joined Aug 2014 · Points: 110

that looks like 80% sending weather to me

Guy Keesee · · Moorpark, CA · Joined Mar 2008 · Points: 310

If you use the "weather forecast" to decide if you should go or not.... you will miss out on good days climbing. 

A old timer once told me: "Only a fool thinks he can predict the weather in the mountains." 

and a 20% chance of rain is a 80% chance of no rain. 

 




 

King Tut · · Citrus Heights · Joined Aug 2012 · Points: 440

Frickin' go dude, there is enough to do in Tuolumne that is shorter if the way the day develops is sketchy. 

Looks like some super fun stuff lower down on the approach:

https://www.mountainproject.com/v/north-buttress-of-cathedral/110900870

Just remember, if you start seeing clouds building while you are at the base, its no go unless dying as a fried egg is your thing.

And the earlier in the day the clouds start building the more likely they will end up producing weather. The summit of Cathedral is no place to be in storm.

Marc801 C · · Sandy, Utah · Joined Feb 2014 · Points: 65
Guy Keesee wrote:

and a 20% chance of rain is a 80% chance of no rain.

Reposting from another thread as it's relevant here:

from: https://www.weather.gov/ffc/pop

CHANCE OF RAIN 40 PERCENT.

What does this "40 percent" mean? ...will it rain 40 percent of of the time? ...will it rain over 40 percent of the area?

The "Probability of Precipitation" (PoP) describes the chance of precipitation occurring at any point you select in the area.

How do forecasters arrive at this value?

Mathematically, PoP is defined as follows:

PoP = C x A where "C" = the confidence that precipitation will occur somewhere in the forecast area, and where "A" = the percent of the area that will receive measureable precipitation, if it occurs at all.

So... in the case of the forecast above, if the forecaster knows precipitation is sure to occur ( confidence is 100% ), he/she is expressing how much of the area will receive measurable rain. ( PoP = "C" x "A" or "1" times ".4" which equals .4 or 40%.)

But, most of the time, the forecaster is expressing a combination of degree of confidence and areal coverage. If the forecaster is only 50% sure that precipitation will occur, and expects that, if it does occur, it will produce measurable rain over about 80 percent of the area, the PoP (chance of rain) is 40%. ( PoP = .5 x .8 which equals .4 or 40%. )

In either event, the correct way to interpret the forecast is: there is a 40 percent chance that rain will occur at any given point in the area.

Guy Keesee · · Moorpark, CA · Joined Mar 2008 · Points: 310

Marc....  I just go no matter what the forecast is. And as King Tut pointed out you need to look around, smell the air, and make a decision.... 

But I find if one sits at home, 250 miles from the action because of a iffy forecast, you have a good chance of your friends returning home only to report... "it was awsome, cool breezes nice cloud cover... one of the best days ever.." 

And anyway TM is really nice even in a downpour.... unless your up 3 pitches. 





Marc801 C · · Sandy, Utah · Joined Feb 2014 · Points: 65
Guy Keesee wrote:

Marc....  I just go no matter what the forecast is. And as King Tut pointed out you need to look around, smell the air, and make a decision....

That's what I've been doing for the past 40 years!

I just thought the explanation of POP interesting since so many people misinterpret it.

 But I find if one sits at home, 250 miles from the action because of a iffy forecast, you have a good chance of your friends returning home only to report... "it was awsome, cool breezes nice cloud cover... one of the best days ever.." 

Yep.

And anyway TM is really nice even in a downpour.... unless your up 3 pitches. 

I recall nearly drowning once in TM. On rappel. On Stately Pleasure Dome. 

dylan grabowski · · Oakland · Joined Mar 2015 · Points: 55

Valid points, gentlemen. En route. 

Cheers!

Guideline #1: Don't be a jerk.

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